Disc drives have utilized circular tracks for recording information on discs having a magnetic coating on the surface. It is a goal of a disc drive designer to provide as much storage capacity as possible. For a given physical structure, this can be accomplished by increasing the amount of data recorded on a track.
The surfaces of each disc have been divided into recording zones and the frequency of recording within a zone is maintained constant in order to maintain a relatively constant bit density across the recording surface. The recording frequency in each zone differs. The recording bit density in each zone is a function of the ratio of the recording frequency over the linear velocity of the rotating disc drive. Thus, the recording bit density in each zone is the same across each disc.
FIG. 1 illustrates the recording zones in a typical hard drive. There is shown a pair of discs 100 and 102 in a disc drive, each disc having recording zones defined as Z1, Z2, and Z3. The zones in the two-disc drive are vertically aligned and the boundaries of the zones are defined radially by the distances indicated by R1-R4 based on the distance from the center C of the disc. The recording frequency used in each zone of each disc is the same. Thus, the recording frequency used in zone Z1 of disc 1 is the same as that used in zone Z1 of disc 2. Furthermore, the recording bit density associated with zone Z1 of disc 1 is the same as that used in zone Z1 of disc 2. The zones are numbered such that the recording frequency decreases as the linear velocity decreases as the zone number increases.
The recording frequency used within each of the zones is determined at the design stage based on various factors, including an expected nominal head read/write performance for the heads to be used in the drive. The performance of each head with its respective surface is measured to determine if it met the minimum performance standard threshold. If any of the heads in a disc array failed to reach at least the minimum threshold, the drive was considered unacceptable and was shipped unless the head could be replaced to meet the minimum performance standard.
The replacement of a failed head can become an expensive task. In some cases, a failed head can miss the minimum performance standard threshold by a slight margin. In these cases, the replacement of the failed head is needless and it is more economically feasible to attempt to accommodate for the lost storage capacity.
Accordingly, there is a need for a mechanism by which the storage capacity associated with a disc drive can be maintained even with read/write heads that do not meet the desired recording bit density thresholds.
The incorporated application discloses the basic concept of recording at different frequencies on different disc surfaces. However, because of the constant demand for increased disc capacity, further optimization of this technique of Variable Bit per Inch (VBPI) Recording is very desirable.